Method of producing biaxially textured buffer layers and related articles, devices and systems

ABSTRACT

A superconductor article includes a substrate and a first buffer film disposed on the substrate. The first buffer film includes a polycrystalline material. An IBAD (ion-beam assisted deposition) second buffer film is disposed on the first buffer film, the second buffer film having a biaxial crystal texture. A superconductor layer can be disposed on the second buffer film.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation-in-part and claims priorityfrom U.S. Utility patent application Ser. No. 10/457,184, filed Jun. 9,2003, entitled “METHOD OF PRODUCING BIAXIALLY TEXTURED BUFFER LAYERS ANDRELATED ARTICLES, DEVICES AND SYSTEMS,” naming inventors David P. Nortonand Venkat Selvamanickam, which application is incorporated by referenceherein in its entirety.

FIELD OF THE INVENTION

The invention relates to biaxially textured buffer layers and articles,devices and systems made therefrom, including superconductor wires andtapes.

BACKGROUND OF THE INVENTION

Much of the effort to develop a high temperature superconducting (HTS)wire or tape has focused on coated conductors based on the epitaxialgrowth of high temperature superconducting (HTS) films on tapes thatpossess a biaxially-textured surface. Superconducting films withcritical current densities in excess of 1 MA/cm² at 77 K and self-fieldhave been achieved for epitaxial YBa₂Cu₃O₇ films on biaxially-texturedtapes produced either by ion-beam assisted deposition (IBAD) orthermomechanically-textured metals.

In previous work involving IBAD, the synthesis of the biaxially-texturedbuffer layer suitable for HTS films capable of carrying high criticalcurrent densities has employed the ion-assist process to produce boththe in-plane and out-of-plane texture. In order to realize an HTS filmpossessing a high critical current on a biaxially textured substrate,the buffer layer architecture should satisfy rigorous requirements. Thegrains within the topmost buffer layer construct desirably provide acommon in-plane and out-of-plane crystallographic texture with a mosaicspread of generally less than 20 degrees, with lower mosaic spreads suchas less than 10 degrees providing better superconducting articles.

The top layer should generally be chemically compatible with thesuperconductor so as to not react during superconductor deposition andbe mechanically robust to prevent microcrack formation at the HTS/bufferlayer interface. To date, biaxially textured buffer layers that have metthese objectives generally rely on the use of the ion-assist (IBAD)process in determining the in-plane and out-of-plane texture. Forexample, biaxially textured yttria-stabilized zirconia (YSZ) bufferlayer can be formed by IBAD with the (100) in-plane and (001)out-of-plane texture by directing an Ar+ beam flux oriented 55 degreesfrom the surface normal, which corresponds to the [111] direction for a(001)-oriented cubic material.

While the above-described IBAD process has provided the desired biaxialtexture requiring a relatively high thickness (>1 μm), such as by use ofa YSZ film deposited in the presence of the Ar+beam, the process isrelatively slow and as a result expensive. The speed and price of suchprocess is a significant issue in the large-scale production ofsuperconducting tapes since it would affect the ability to produce alow-cost HTS tape. A second approach involves the IBAD deposition of MgOrequiring a sub-10 nm control of the nucleation process, typicallyemploying an in-situ monitoring technique, such as reflection highenergy electron diffraction, for controlling the crystallographictexture. This approach is difficult to employ for large-scaleproduction. Also, the quality of MgO films deposited by IBAD has beenfound to be extremely sensitive to minor variations in the processes andstructures used for this material.

Accordingly, there is a need in the art for improved superconductorcomponents, including coated HTS conductors, processes for forming same,and articles incorporating same. In particular, there is a need forcommercially viable HTS conductors having characteristics enhancinglarge-scale production, and processes for forming the same.

Accordingly, there is also a need in the art for an alternativetechnique that would require less thickness than that required for IBADof YSZ, but would be more robust and less sensitive than the IBADprocess for MgO.

SUMMARY OF THE INVENTION

According to one embodiment, a superconductor article includes asubstrate and a first buffer film disposed on the substrate, a secondbuffer film disposed on the first buffer film and a superconductor layeroverlying or disposed on the second buffer film. The first buffer filmhas a polycrystalline structure, and may be a polycrystalline oxide thinfilm material. The second buffer film includes a material from the groupconsisting of IBAD MgO, IBAD CeO₂, or IBAD RE₂O₃, where RE is a rareearth element, and having a biaxial crystal texture.

In another embodiment, a superconductor article is provided, including asubstrate, a first buffer film disposed on said substrate, the firstbuffer film comprising a polycrystalline material having the rocksalt-like crystal structure, and a second buffer film disposed on saidfirst buffer film. The second buffer film includes a material from thegroup consisting of IBAD MgO, IBAD CeO₂, or IBAD RE₂O₃, where RE is arare earth element, and having a biaxial crystal texture. Thesuperconductor article further includes a superconductor layer disposedon said second buffer film

In one embodiment, the first buffer film has a uniaxial crystal texturecharacterized by (i) texture in a first crystallographic direction thatextends out-of-plane of the first buffer film with no significanttexture in a second direction that extends in-plane of the first bufferfilm, or (ii) texture in a first crystallographic direction that extendsin-plane of the first buffer film with no significant texture in asecond direction that extends out-of-plane of the first buffer film.

As used herein, the term “disposed on” is used to refer to the relativelocation of the elements in an article, and does not necessarily requiredirect contact between the described elements or components (unlessotherwise described as such), and may include intervening layers orfilms. Accordingly, the term is used in a general sense regardingorientation or location, as generally illustrated in the drawings. Forexample, a protective layer can be disposed between the substrate andthe first buffer film.

The uniaxially textured crystallographic direction of the first bufferfilm can be in-plane or out-of-plane. In the case of out-of-planetexture, the out-of-plane crystal texture can be generally aligned alongthe [001] crystal direction. The out-of-plane texture can have a mosaicspread no more than about 30 degrees, preferably no more than about 20degrees, or more preferably no more than about 10 degrees.

The first buffer film can have a rock-salt-like crystal structure or mayexhibit anisotropic growth habits. The first buffer film can includeREBa₂Cu₃O₇, Bi₄Ti₃O₁₂, MgO or NiO. The substrate can be a metal alloy,such as a Ni-based alloy.

The biaxially textured second buffer film can be aligned along a firstaxis along the [001] crystal direction, and along a second axis having acrystal direction selected from the group consisting of [111], [101],[113], [100], and [010]. The second buffer film can have arock-salt-like crystal structure. In this embodiment, the second bufferfilm can be MgO, NiO, YSZ, CeO₂, Y₂O₃, TiO₂, SnO₂, Mn₃O₄, Fe₃O₄, Cu₂O orRE₂O₃, where RE is a rare earth element.

The superconductor article can provide a Jc of at least 0.5 MA/cm² at 77K and self-field, and preferably at least 1.0 MA/cm² at 77 K andself-field. The superconductor layer can comprise REBa₂Cu₃O₇, where REis a rare earth element. RE can comprise Y. The superconductor articlecan comprise a superconductor tape.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates a superconducting tape article, according to anembodiment of the invention;

FIG. 2 illustrates a power cable, according to an embodiment of theinvention;

FIG. 3 illustrates details of a single exemplary superconducting cable,according to another embodiment of the invention;

FIG. 4 illustrates a power transformer, according to yet anotherembodiment of the invention;

FIG. 5 illustrates a power generator, according to an embodiment of theinvention; and

FIG. 6 illustrates a power grid, according to another embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention provide a novel HTS article,methods for forming same, and devices and systems incorporating thesame. According to one feature, a method is provided for forming abiaxially textured buffer layer article using a two-step process andassociated articles, devices and systems. The first step provides afirst buffer film having a polycrystalline structure, such as apolycrystalline oxide and/or a polycrystalline rock salt-like crystalstructure.

The first buffer layer may have a uniaxial texture, typicallycharacterized by (i) texture in a first crystallographic direction thatextends out-of-plane of the first buffer film with no significanttexture in a second direction that extends in-plane of the first bufferfilm, or (ii) texture in a first crystallographic direction that extendsin-plane of the first buffer film with no significant texture in asecond direction that extends out-of-plane of the first buffer film. Thesingle crystallographic direction can be one of an in-plane direction oran out-of-plane direction, wherein the other crystallographic directionshas no significant crystallographic texture. Thus, the uniaxiallytextured first buffer film does not provide biaxial texture.

According to one embodiment the uniaxial crystal texture extendsout-of-plane, with no significant texturing in-plane. Typically, it isconsidered that ‘in-plane’ is defined by two mutually perpendiculardirections in the plane of the buffer film. According to anotherembodiment, the uniaxial crystal texture extends in one of the in-planedirections, with no significant texturing out-of-plane, and no texturingin the mutually perpendicular in-plane direction. As used herein, theterm “texture”, whether referring to in-plane or out-of-plane texture,refers to a grain-to-grain crystallographic misorientation “mosaicspread” of the respective layer. Typically, the mosaic spread for atextured layer is less than about 30 degrees, such as less than about 20degrees, 15 degrees, 10 degrees, or 5 degrees, but is generally finitetypically being greater than about 1.degree. According to oneembodiment, the term “no significant texture,” generally refers to agrain-to-grain misorientation “mosaic spread” of the respective layerbeing greater than about 30 degrees and including generally randompolycrystalline arrangements.

Regarding the out-of-plane crystallographic texture, the mosaic spreadis generally represented by a full-width-at-half-maximum value of anx-ray diffraction peak, such as obtained by a (001) pole figuremeasurement. In this case, the (001) crystallographic planes of thegrains are aligned and thus textured in a direction perpendicular to thenormal to the film within an angular spread of less than about 30degrees.

While the foregoing has focused particularly on one embodiment in whichthe polycrystalline first buffer film has a uniaxial texture, accordingto another embodiment, the first buffer film may comprise ananocrystalline buffer film. As used herein, ‘nanocrystalline’ refers toa film composes primarily of fine crystallites having an averagecrystallite size within a range of about 0.1 to about 50 nanometers,generally about 1 to 20 nanometers, and certain embodiments within arange of about 1 to 10 nanometers. Particular embodiments herein have anaverage crystallite size of about 5 nanometers. Generally thefirst-buffer film is primarily crystalline, that is, is primarilynanocrystalline, but may have a minority content of amorphous regions.More typically, the first buffer film is at least 75% (as characterizedby TEM analysis) nanocrystalline, more typically at least 80%nanocrystalline. The foregoing buffer film is accurately described aspolycrystalline, since the primary phase is crystalline rather thandisordered (i.e., amorphous), amorphous buffer films being alreadyunderstood in the art. The present nanocrystalline buffer film isparticularly advantageous over prior amorphous films. For example,improvements in crystallography, e.g., reduction in crystallographictilt of overlying layers (e.g., the biaxially textured film) overamorphous layers may be realized. Additional details of nanocrystallinebuffer layers may be reviewed in US 2003/0144150 A1, published Jul. 31,2003, incorporated herein by reference thereto.

The first buffer film formed of nanocrystalline material may be chosenfrom several compositions. For example, the nanocrystalline material maybe selected from the group consisting of Type C rare-earth oxides suchas yttria and Gd₂O₃, fluorites such as zirconia and ceria, spinel suchas nickel aluminate, and pervoskites such as barium zirconate.

A second buffer film is disposed on the first buffer film, the secondbuffer film having a biaxial crystal texture. A biaxially texturedsecond buffer film by definition has both in-plane and out-of-planecrystal texture. A biaxially textured layer is defined herein as apolycrystalline material in which both the crystallographic in-plane andout-of-plane grain-to-grain misorientation of the topmost layer is lessthan about 30 degrees, such as less than about 20 degrees, 15 degrees,10 degrees, or 5 degrees, but is generally finite typically greater thanabout 1.degree. The degree of biaxial texture can be described byspecifying the distribution of grain in-plane and out-of-planeorientations as determined by x-ray diffraction. Afull-width-half-maximum (FWHM) of the rocking curve of the out-of-plane(.DELTA..theta.) and in-plane (.DELTA..phi.) reflection can bedetermined. Therefore, the degree of biaxial texture can be defined byspecifying the range of .DELTA..phi. and .DELTA..phi. for a givensample.

The first buffer film having a uniaxial texture is generally formedwithout the use of an ion beam while the second step which forms thesecond buffer layer film uses an ion-beam assisted deposition (IBAD)process to produce a biaxially textured layer portion on top of thefirst buffer layer portion. The ability to obtain a biaxially texturedbuffer surface using IBAD without the associated manufacturing issuesrelating to use of IBAD for the entire buffer layer can produce highperformance articles substantially more efficiently and economically ascompared to conventional IBAD processing. Embodiments of the presentinvention thus attenuate the general use of IBAD processing to produce abiaxial texture in the full buffer layer thickness, and additionally,reduce the need for highly controlled IBAD processing conditions, sincelower process tolerances can be accepted, which is preferable in amanufacturing environment. Again, in the context of uniaxially texturedfirst buffer films, this is believed to be due to the concept that it isenergetically favorable, from a crystal nucleation and growth viewpoint,for the deposited material to align along the uniaxial crystallographicdirection during deposition, creating more flexibility in IBAD filmprocessing.

A biaxially textured electronically active layer can be disposed on thebiaxially textured buffer layers formed according to embodiments of theinvention. The electronically active layer may be a superconductor, asemiconductor, a photovoltaic, a ferroelectric or an optoelectric, orany other electromagnetic device wherein grain boundary control isimportant. In this regard, aspects of the present invention areparticularly suitable for providing high temperature supercondutorcomponents, in which the electronically active layer is formedprincipally of a superconducting material. Aspects of the invention areparticularly well suited for the formation of electronically active wireand tape (hereafter a “tape”) articles which have biaxial texture. Asused herein, the term “tape” refers to an article having an aspect rationot less than about 1,000, the aspect ratio meaning the ratio of longestdimension (length) to next longest dimension (width). Typically, theaspect ratio is greater than about 10⁴, and even greater than about 10⁵.

The biaxially textured buffer layers are suitable for the formation of ahigh temperature superconducting article which provides a criticalcurrent density in excess of about 0.5 MA/cm² at about 77 K andself-field, and preferably in excess of about 1 MA/cm2. Embodiments ofthe invention is also useful for a variety of other electronicapplications in which sharp crystallographic texture is important.

FIG. 1 shows a tape article 10 according to an embodiment of theinvention having a multi-layer composition including a texturedsuperconductor tape 18 having biaxial texture along its entire length.The tape article 10 is expected to be particularly useful for increasingthe current carrying capability and reducing AC resistive losses ofpower transmission lines. Superconductor article 10 consists of asubstrate 12. The substrate 12 can be a metal or polycrystallineceramic. In case of a metal, the substrate 12 can be an alloy, such as aNi-based alloy. Texture in the substrate 12 is generally not required.Thus, substrate 12 can be polycrystal line or amorphous. Polycrystallinesubstrates may be utilized for some applications requiring certainthermal, mechanical, and electrical properties offered by suchmaterials, such as commercially available Ni-based alloys, such as theHastelloy group of high performance substrate materials. The substrate12 provides support for the superconductor article 10, and can befabricated over long lengths and large areas using the aspects of thepresent invention. When the superconductor tape is of long length (e.g.1 km), first buffer layer 14 and second buffer layer 16 may be depositedon biaxially-textured substrate surface 12 using a suitable translationprocess, such as reel-to-reel translation.

Optional protective layer 13 is generally polycrystalline and isdisposed on the top surface of substrate 12. Protective layer 13 ispreferably used when buffer layer 14 is chemically incompatible withsubstrate 12. The polycrystalline protective layer is preferably anoxide, such as cerium oxide or yttria-stabilized zirconia (YSZ).

A second buffer layer 16 is disposed on the first buffer layer 14. Asmentioned above, the first buffer layer 14 may provide texture in afirst crystallographic direction that extends out-of-plane of the firstbuffer film with no significant texture in a second direction thatextends in-plane of the first buffer film, or (ii) texture in a firstcrystallographic direction that extends in-plane of the first bufferfilm with no significant texture in a second direction that extendsout-of-plane of the first buffer film, while second buffer layer 16provides biaxial texture. Alternatively, the first buffer layer 14 maybe nanocrystalline. Epitaxially-grown superconducting layer 18 isdisposed on biaxially texture buffer layer 16.

Although not shown in FIG. 1, at least one epitaxial film can beprovided between the second buffer layer 16 and the superconductor layer18. In addition, a noble metal layer can overlay the superconductorlayer 18, such as Ag.

First buffer layer 14 may be achieved either through the anisotropicgrowth habits of selected materials or by preferential selection ofenergetically favorable growth orientations of selected materials. Thefirst buffer film 14 maybe provided without the need for ion assist andis referred to as Layer 1. For example, Layer 1 can be a polycrystallinematerial, such as those having an energetically favorable growthdirection <100>along the film normal. Examples are rock-salt structuressuch as MgO and NiO, which have a tendency to align preferentially inthe energetically favorable direction of <100>irrespective of theunderlying substrate orientation. U.S. Pat. No. 6,190,752 to Do et al.entitled “Thin films having rock-salt-like structure deposited onamorphous surfaces” provides detailed information regarding rock-saltstructures and available species.

Several polycrystalline thin-film materials, including various oxides,are suitable for buffer layer 14, including those for suitablenanocrystalline formation and those for uniaxial texturing such as thosewith anisotropic growth habits, which tend to align a specificcrystallographic axis along the surface normal of a substrate forcertain deposition conditions. In terms of anisotropic growth, severalmulti-cation oxides can be used. For example, the use of REBa₂Cu₃O₇,where RE is a rare earth element such as YBa₂Cu₃O₇, and Bi₄Ti₃O₁₂, andwherein both exhibit out of plane (c-axis) oriented film growth onrandomly oriented substrates. Uniaxially textured films can be used asbuffer layer 14 which can act as an initial template for epitaxialgrowth (including IBAD films) to form biaxially textured buffer layer16. Buffer layer 14 generally has a thickness within a range about 100to about 3000 Angstroms. Buffer layer 14 is preferably aligned along the[100] direction and can be deposited by sputtering, pulsed laserdeposition, or evaporation.

Second buffer layer 16 is a layer in which in-plane texture is generallyinduced due to the ion beam and is also referred to herein as Layer 2.By imposing an ion beam (e.g. Ar) along a high-symmetry direction ofbuffer layer 16 during epitaxy of buffer layer 16, the growth of grainsoriented with a preferred axis aligned along the ion beam direction aregenerally preferred over those grains with other orientations. Thissubsequent IBAD growth induces an in-plane texture component in bufferlayer 16 that does not exist in buffer layer 14 (in the case of auniaxial textured buffer layer 14), while still maintaining theout-of-plane texture.

The second buffer layer 16 generally has a thickness within a range ofabout 100 to about 5000 Angstroms. The superconductor layer 18 thicknessis generally from about 500 to about 10,000 nm. The biaxially texturedsecond buffer layer 16 is preferably aligned along a first axis havingalong a [001] crystal direction, and along a second axis having acrystal direction selected from the group consisting of [111], [101],[113], [100], and [010]. The second buffer layer 16 can have arock-salt-like crystal structure and comprise MgO, NiO or be selectedfrom YSZ, CeO₂, Y₂O₃, TiO₂, SnO₂, Mn₃O₄, Fe₃O₄, CU₂O, or RE₂O₃, whereinRE is a rare earth element. Buffer layer 16 can be deposited bysputtering or evaporation.

Superconductor layer 18 is preferably an oxide superconductor. The oxidesuperconductor is preferably selected from REBa₂Cu₃O₇ where RE is a rareearth element, such as Y, and related compounds. The superconductorarticle 10 can provide a Jc of at least about 0.5 MA/cm² at about 77 Kand self-field, and preferably at least about 1 MA/cm².

Although aspects of the invention are generally described using apolycrystalline thin film 14, particularly a c-axis textured firstbuffer layer, the invention is in no way limited to this embodiment, andspecifically includes nanocrystalline materials. In one embodiment ofthe invention, the uniaxial crystal structure in the first buffer film14 could also be along one direction within the plane of the film(a-axis or b-axis). In this embodiment, there is no preferential texturein a plane perpendicular to the axis along which the crystals aretextured within the film plane (c-axis). One example of this embodimentis that of fiber texture, where a preferential uniaxial texture ispresent along the long direction of a tape or a wire but no preferentialtexture is present in the plane perpendicular to this direction.

A general embodiment of the invention involves providing a substrate forfilm growth. The substrate is cleaned with solvents, such as acetone,methanol, and trichloroethylene. The substrate is mounted in adeposition chamber suitable for thin film deposition. A polycrystallineprotective layer is then optionally deposited on the substrate. Thepolycrystalline layer prevents a chemical reaction from occurringbetween Layer 1 and the substrate.

The protective layer coated substrate is heated in an ambient suitablefor the deposition of an anisotropic thin film or a thin film whoseenergetically favorable growth direction is <100>(layer 1). Layer 1 isthen deposited and provides out-of-plane (c-axis) texture without theneed for ion assist. The Layer 1 coated substrate is then transferred toa thin-film deposition system equipped with an ion gun. The substrate isheated to a temperature suitable for the epitaxial growth of Layer 2 onLayer 1. Vacuum deposition is employed to deposited Layer 2 on Layer 1in the presence of the ion beam, which is directed along a preferredcrystallographic direction of the material constituting Layer 2 toinduce in-plane texture during epitaxy.

The invention is useful for a wide variety of applications, particularlysuperconductor applications. Regarding superconductor applications, theinvention can be used to form high temperature superconducting wires ortapes which can be used for transmission lines, motors, generators, orhigh-field magnet applications.

FIG. 2 illustrates a power cable 200, according to an embodiment of theinvention. Power cable 200 shown includes three superconducting cables220 arranged in a trefoil arrangement where all three phases are housedin the same thermally insulating conduit 230. Ground plane 240 is alsoshown. The phases are situated as close together as physically possible.Although not shown, other arrangements are possible, including aconcentric arrangement where the 3 cables are situated concentrically.

FIG. 3 shows details of a single exemplary superconducting cable 220.Proceeding from the outside to the inside of cable 220, cable 220includes enclosure 366, skid wires 364, corrugated steel 362 and thermalinsulator 360. LN₂ duct 358 provides refrigerant to cable 220 and isdisposed on centering wires 356. Copper shield 354 is provided and isdisposed on superconductor tape layer 352. Dielectric tape 350 isdisposed between tape layer 352 and copper shield 348. Anothersuperconductor tape layer 346 is beneath copper shield 348. Former/duct344 provides a passage of coolant fluid, such as liquid nitrogen (LN₂)refrigerant which permits inexpensive cooling to temperatures above thefreezing point for nitrogen (which is at about 63.3 K). The power cable200 can be used as a power transmission cable or a power distributioncable.

FIG. 4 illustrates power transformer 400, according to anotherembodiment of the invention. Power transformer 400 includes a primarywinding 472, a secondary winding 474 and core 476. At least one of theprimary winding 472 and secondary winding 474 comprises a wound coil ofsuperconductive tape as described above embedded in an insulatingmaterial such as epoxy. The secondary winding 474 can have fewer or morewindings as compared to the primary winding 472.

FIG. 5 illustrates power generator 500, according to an embodiment ofthe invention. Power generator 500 includes a turbine 582 and a shaft584 coupled to a rotor 586 comprising electromagnets comprising rotorcoils, and a stator 588 comprising a conductive winding surrounding therotor, wherein at least one of the winding and the rotor coils comprisesa superconductive tape as described above.

FIG. 6 illustrates a power grid 600, according to another embodiment ofthe invention. Power grid 600 includes a power generation stationcomprising a power generator plant 690 and transmission lines 692 todeliver power to transmission substation 694. Transmission substation694 includes transformers 695. Power transmission cables 696 emanatefrom transmission substation 694. Power transmission cables 696 deliverpower from transmission substation 694 to power substation 698 whichincludes a plurality of power transformers 697 for stepping-down voltagefor distribution. Power distribution cables 610 deliver power from powersubstation 698 to end users 602. At least one of the power distributioncables 610, power transmission cables 696, transformers 697 of the powersubstation 698, transformers of the transmission substation 695, and thepower generator plant 690 comprise a plurality of superconductive tapesas described above.

EXAMPLES

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication. The invention can take other specific forms withoutdeparting from the spirit or essential attributes thereof.

Example 1

A Ni-based alloy substrate is provided for film growth. The substrate iscleaned with solvents, such as acetone, methanol, and trichloroethylene.The substrate is mounted in a pulsed-laser deposition chamber for thinfilm deposition. A polycrystalline yttria-stabilized zirconia (YSZ)protective layer is deposited on the substrate using pulsed laserdeposition at about 25.degree. C. under vacuum. This protective layerprevents chemical reactions between layer 1 and the substrate.

The coated substrate is heated to about 700.degree. C. in vacuum for thedeposition of an YBa₂Cu₃O₇ thin film (Layer 1). A YBa₂Cu₃O₇ film ofthickness about 300 nm is deposited at about 700.degree. C. in about 200mTorr of oxygen. The film is c-axis oriented, but randomly orientedin-plane. The substrate is then transferred to a thin-film depositionsystem equipped with an ion gun. The substrate is heated to atemperature suitable for the epitaxial growth of MgO on YBa₂Cu₃O₇ onLayer 1. Pulsed laser deposition is employed to deposit epitaxial MgO onthe YBa₂Cu₃O₇ template. The MgO layer will be (001) textured. This isfollowed by the growth of CeO₂ in the presence of an Ar ion beam, whichis directed along either the [111] or [110] crystallographic directionof CeO₂.

Example 2

A Ni-based alloy substrate is provided for film growth. The substrate iscleaned with solvents, such as acetone, methanol, and trichloroethylene.The substrate is mounted in a pulsed-laser deposition chamber for thinfilm deposition. A MgO film of thickness of about 100 nm (Layer 1) isdeposited at about 25.degree. C. in vacuum. The MgO layer will be (001)textured. The coated substrate is then transferred to a thin-filmdeposition system equipped with an ion gun. A second layer of MgO (Layer2) is grown in the presence of an Ar ion beam, the ion beam beingdirected along either the [111] or [110] crystallographic direction ofMgO. The second MgO layer (Layer 2) will be biaxially textured.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof may be made by persons skilled in the artwithout departing from the scope of the present claims.

1. A superconductor article, comprising: a substrate; a first bufferfilm disposed on said substrate, said first buffer film comprising apolycrystalline oxide thin film material; a second buffer film disposedon said first buffer film, said second buffer film comprising a materialfrom the group consisting of IBAD MgO, IBAD CeO₂, or IBAD RE₂O₃, whereRE is a rare earth element, and having a biaxial crystal texture; and asuperconductor layer disposed on said second buffer film.
 2. The articleof claim 1, wherein the second buffer film comprises IBAD MgO.
 3. Thearticle of claim 1, wherein the first buffer film comprises ananocrystalline material.
 4. The article of claim 3, wherein thenanocrystalline material is selected from the group consisting of Type Crare-earth oxides, fluorites, spinels, and pervoskites.
 5. The articleof claim 4, wherein the nanocrystalline material comprises yttria. 6.The article of claim 3, wherein the nanocrystalline material has anaverage crystallite size within a range of about 0.1 to about 50 nm. 7.The article of claim 6, wherein the nanocrystalline material has anaverage crystallite size within a range of about 1 to about 20 nm. 8.(canceled)
 9. (canceled)
 10. A superconductor article, comprising: asubstrate; a first buffer film disposed on said substrate, said firstbuffer film comprising a polycrystalline material having the rocksalt-like crystal structure; a second buffer film disposed on said firstbuffer film, said second buffer film comprising a material from thegroup consisting of IBAD MgO, IBAD CeO₂, or IBAD RE₂O₃, where RE is arare earth element, and having a biaxial crystal texture; and asuperconductor layer disposed on said second buffer film.
 11. Thearticle of claim 10, wherein the polycrystalline material has the rocksalt crystal structure.
 12. The article of claim 10, wherein the secondbuffer film comprises IBAD MgO.
 13. (canceled)
 14. (canceled)